The present invention relates to a switch device that includes an activation mechanism for directly activating a bimetallic plate and involves a compact and simple structure.
A conventional switch device, especially for those switches comprising a bimetallic plate to prevent burnout when overloading occurs, is disclosed in U.S. Pat. Nos. 4,167,720, 4,937,548, 5,223,813, 5,451,729 and 5,558,211. These switches commonly involve a complicated structure and are composed of a large number of components/parts, meaning they have high risk of malfunctioning. Besides, the bimetallic plate is indirectly activated by a toggle so that the metallic plate is activated for a period of time after the action on the toggle is completed. This very short period of time could result in burnout of the switch device in an overload of the current FIGS. 1-3 of the attached drawings show the device disclosed in U.S. Pat. No. 5,223,813, and the switch member 101 is connected to a link 102 that is then connected to an arm 103. The bimetallic plate 104 is compressed by the arm 103 and is deformed when the arm 103 is activated by the link 102 and the switch member 101. The direct pressure on the metallic plate 104 from the arm 103 may break the metallic plate 104 and the reaction of the metallic plate 104 is slower than being expected.
Therefore, it is desired to have an activation mechanism for the switch device wherein the metallic plate is not directly pressed by any part in the switch device so as to improve the shortcomings of the conventional switch devices.
In accordance with an aspect of the present invention, there is provided a switch device comprising a casing having a path defined therein and a protrusion is surrounded by the path. Two first terminals extend from a bottom of the casing and one of which has a first contact point.
A push member is movably engaged on a top of the casing and two positioning springs are biased between the push member and the casing. A guide pin is pivotably connected to the push member and includes an insertion that is movably engaged with the path in the casing. A bimetallic plate has an end connected to the other terminal and includes a free section. A second contact point is connected to the free section and located above the first contact point.
A driving plate is rotatably connected to the casing and includes a polygonal aperture through which the insertion of the guide pin and the protrusion extend. A convex portion extends from an inner periphery of the aperture. A hook portion extends from the driving plate and holds a free end of the bimetallic plate.
The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention.